Exploring semiconductor and superconducting photodetectors in quantum technologies
The manipulation and measurement of photons, individual quanta of light, underpin the promising emerging technologies of photonic quantum computing and quantum communications.
However, without a reliable and scalable photodetector solution, they cannot reach their full potential. Furthermore, creating a scalable, high-performance single-photon detector solution unlocks a range of other lucrative applications, including biological imaging, LiDAR, gas sensing, and quantum imaging.
Two types of single-photon detector technology are competing to become the industry standard in both fields: semiconductor detectors, such as single-photon avalanche diodes (SPADs), and superconducting detectors including superconducting nanowire single-photon detectors (SNSPDs). IDTechEx's new report, "Quantum Sensors Market 2025-2045: Technology, Trends, Players, Forecasts", outlines this competition alongside insights and market forecasts for the wider quantum sensing market.
What is a single-photon detector?
Fundamentally, all types of single-photon detectors convert an incoming photon of light into an electrical signal. The field of single-photon detectors can be split generally into semiconductor-based and superconducting detectors, where SPADs and SNSPDs are the respective frontrunners from each group.
For SPADs, measuring individual photons is achieved through a semiconductor PN junction biased beyond its breakdown voltage, such that a single incident photon causes an 'avalanche' of hundreds or even thousands of electrons, measured as a well-resolved signal pulse.
SNSPDs meanwhile, are formed of a thin, snaking nanowire of superconducting material, typically cooled cryogenically to less than 3K. An incident photon disrupts the superconductivity and creates a resistive 'hotspot', which causes a spike in the voltage across the detector.
Not all single-photon detectors are created equal
Two of the most important metrics for the performance of a single-photon detector are the detector efficiency and dark count rate (a measure of noise in the system). Generally, SNSPDs perform better on both metrics, with >90% detector efficiency and 100Hz for SPADs.
However, the fundamental drawback of superconducting detectors such as SNSPDs is that they must always be cooled to very low temperatures. This typically involves bulky, expensive, and power-hungry cryostats. Currently, the scale and funding available for quantum technology projects makes it feasible to use these cryogenics, and developing more efficient refrigerators is a top priority for key players such as Single Quantum and PsiQuantum. The ultra-low noise of SNSPDs is largely due to their very low operating temperature, and players backing superconducting detectors long-term believe this will always be essential.
SPADs meanwhile have the potential to enable room-temperature quantum technologies, with innovations in semiconductor materials and consistent improvements in their performance over recent years. Cooling can also reduce their dark count rate, but it is not a prerequisite for their operation. IDQuantique has commercialized a line of low-noise and low-jitter photodetectors using cooled InGaAs/InP SPADs. The primary application is in quantum communication schemes such as quantum key distribution (QKD), in which IDQ themselves are currently positioned as a market leader. However, they also produce a line of SNSPD detectors for QKD and quantum research.
Meanwhile, the GB£1.5 million Innovate UK MARCONI project seeks to develop both a SPAD and SNSPD solution to develop a scalable national QKD network for information security purposes. The SPAD solution will be a cheaper detector for short-range QKD while the SNSPD will perform better for long-range communications. It remains to be seen if SPADs and SNSPDs will truly complement each other in developing quantum communications networks in the long term or if players are simply hedging their bets.
Conclusions and market outlook
Ultimately, the choice between semiconductor and superconducting detectors will be decided by whether it is easier to compromise in cost, scalability or performance. The intrinsically low noise of cryogenically cooled superconducting detectors has made them more popular for research and early-stage products. However, economies of scale and advancements in alternative semiconductors could swing the balance in favor of SPADs and other semiconductor platforms.
For photonic quantum computing, scalability will be essential as the number of qubits per computer increases. PsiQuantum are currently focused on integrating superconducting detectors into photonic chips and building large-scale cryostats. With semiconductor detectors however, photonic quantum computing could become one of the most promising room-temperature platforms. In a way, the compromise in detector choice between fidelity and scalability here mirrors the more general meta-trend of the quantum computing industry in deciding between many noisy qubits or fewer high-quality qubits.
Further insights and analysis of SPADs, SNSPDs, and the larger quantum sensing market can be found in IDTechEx's new report, www.IDTechEx.com/QuantumSensors.
(Author: Noah El Alami, Technology Analyst at IDTechEx)
